This invention relates to compositions comprising spent oil shale, and their use. More specifically, this invention relates to aqueous slurries of spent oil shale including use of such slurries to form coherent masses having mechanical strength.
Numerous hydrocarbonaceous materials are found in underground deposits; for example crude oil, coal, shale oil, tar sands, and others. One method of recovering energy or hydrocarbon from such underground deposits is by underground combustion. An oxidizing gas such as air can be provided to an underground combustion or retorting zone so as to combust a portion of the combustible material contained therein and free hydrocarbon or thereby form materials which are suitable for energy recovery. For example, air or oxygen, and diluent gases such as steam, can be passed into a coal deposit so as to form off-gases having combustible materials such as light hydrocarbons and carbon monoxide. These gases can then be combusted directly for heat, or energy recovered such as through power generation. Underground combustion can be used in the recovery of petroleum crude oil from certain types of deposits. Air or oxygen, and steam, is passed into an underground deposit and combustion initiated so hot combustion gases will aid in the recovery of such crude oil. Similar technique can be used in the recovery of oil from tar sands. One important use of underground combustion is in the recovery of oil from oil shale.
The term "oil shale" refers to sedimentary deposits containing organic materials which can be converted to shale oil. Oil shale can be found in various places throughout the world, especially in the United States in Colorado, Utah, and Wyoming. Some especially important deposits can be found in the Green River formation in the Piceance Basin, Garfield and Rio Blanco counties, in Northwestern Colorado.
Oil shale contains organic material called kerogen which is a solid carbonaceous material from which shale oil can be produced. Commonly oil shale deposits have variable richness of kerogen content, the oil shale generally being stratified in horizontal layers. Upon heating oil shale to a sufficient temperature, kerogen is decomposed and liquids and gases are formed. Oil shale can be retorted to form a hydrocarbon liquid either by in situ or surface retorting. In surface retorting, oil shale is mined from the ground, brought to the surface, and placed in vessels where it is contacted with hot retorting materials, such as hot shale or gases, for heat transfer. The hot retorting solids or gases cause shale oil to be freed from the rock. Spent retorted oil shale which has been depleted in kerogen is removed from the reactor and discarded. Some well-known methods of surface retorting are the Tosco, Lurgi, and Paraho processes and fluid bed retorting.
Another method of retorting oil shale is the in situ process. In situ retorting of oil shale generally comprises forming a retort or retorting area underground, preferably within the oil shale zone. The retorting zone can be formed by mining an access tunnel to or near the retorting zone and then removing a portion of the oil shale deposit by conventional mining techniques. About 2 to about 50 percent, preferably about 15 to about 45 percent, of the oil shale in the retorting area is removed to provide void space in the retorting area. The oil shale in the retorting area is then rubblized by well-known mining and blasting techniques to provide a retort containing rubblized shale for retorting. In some cases it is possible to rubblize underground oil shale without removal of a portion of the oil shale. However, it is generally preferable to remove material so as to provide void space which will result in more uniform rubblization and more efficient use of explosives.
A common method for forming the underground retort is to undercut the deposit to be retorted and remove a portion of the deposit to provide void space. Explosives are then placed in the overlying or surrounding oil shale. These explosives are used to rubblize the shale, preferably forming a zone of rubble having uniform particle size and void spaces. Some of the techniques used for forming the undercut area and the rubblized area are room and pillar mining, sublevel caving, crater retreat and the like. Because of the stratification of oil shale it may be desirable to selectively mine material based on its mineral or kerogen content for removal from the retorting zone. Also because of the stratification, the retorting zone may contain lean oil shale, or rock containing essentially no kerogen. After the underground retort is formed, the pile of rubblized shale is subjected to retorting. Hot retorting gases are passed through the rubblized shale to effectively form and recover liquid hydrocarbon from the oil shale. This can be done by passing a gas comprising air or air mixed with steam through the deposit. Air can be forced into one end of the retort and a fire or flame front initiated. Combustion can be initiated by introducing fuels such as natural gas, propane, shale oil, and the like which are readily combustible with air. After combustion has been initiated, it can be sustained by combusting coke or spent or partially spent oil shale, oxygen contacting the coke forming or maintaining a flame front. This flame front is then passed slowly through the rubblized deposit to effect the retorting. Actually the hot combustion gases passing ahead of the flame front cause the retorting of oil shale and the formation of shale oil. Another suitable retorting fluid comprises hot combustion or retorting off-gas from the same or nearby underground retort. Not only is shale oil effectively produced, but also a mixture of off-gases is produced during retorting. Generally a mixture of off-gases, water and shale oil are recovered from the retort. This mixture undergoes preliminary separation commonly by gravity to separate the gases from the liquid oil from the liquid water. The off-gases commonly also contain entrained dust, and hydrocarbons, some of which are liquid or liquefiable under moderate pressure.
A number of patents describe methods of in situ retorting of oil shale, such as Karrick, L. C., U.S. Pat. No. 1,913,395; Karrick, S. N., U.S. Pat. No. 1,919,636; Uren, U.S. Pat. No. 2,481,051; Van Poollen, U.S. Pat. No. 3,001,776; Ellington, U.S. Pat. No. 3,586,377; Prats, U.S. Pat. 3,434,757; Garrett, U.S. Pat. No. 3,661,423; Ridley, U.S. Pat. No. 3,951,456; and Lewis, U.S. Pat. No. 4,017,119 which are hereby incorporated by reference and made a part hereof.
When oil shale is mined, brought to the surface, and retorted above ground, a large volume of spent oil shale is formed which creates a disposal problem. Often, this spent shale has relatively small particle size which makes dumping undesirable from an aesthetic and environmental viewpoint.
After an underground in situ oil shale retort is burned, the volume of spent shale within the retort has diminished somewhat and commonly does not adequately support the overlying structure. This lack of support can lead to surface subsidence.
When a series of underground in situ oil shale retorts are formed in an oil shale field, it is common to leave substantial areas of intact oil shale between these retorts in order to preserve the structural integrity of the retorts and to control the flow of gases, water, and the like.
Knepper et al., U.S. Pat. No. 4,120,355 and Watson et al., U.S. Pat. No. 4,131,416, teach the introduction of aqueous slurries of spent oil shale from surface retorting into spent subterranean in situ oil shale retorts to form mechanically strong structures. These structures can prevent surface subsidence above the retort, and prevent leaching of chemicals from the mass of rubblized spent shale underground.
Knepper et al. teach that materials can be added to the slurry of water and spent shale from surface retorting in order to modify various properties of the slurry or the solidified mass formed by the slurry. Additives can be used to modify the slurry viscosity or adjust the permeability to water or gas. Plasticizers such as clays, soaps, cement, methyl ethyl cellulose can be added. Clay, such as bentonite or montorillinite can be added. Retarders such as glue, gypsum, lignin and the like can be added to stop flash set or prevent premature solidification of the slurry.
O'Neal, U.S. Pat. No. 3,459,003 teaches the use of slurries of spent shale from surface retorting and water, and in some cases cement, for forming of a competent mass having structural strength underground.
Fondriest, U.S. Ser. No. 803,730, filed June 6, 1977, teaches the use of concrete, sometimes containing spent oil shale from surface retorting, to fill underground voids formed from the mining of oil shale or coal. The concrete forms load bearing pillars so that support pillars of hydrocarbonaceous material can be removed.
Aqueous slurries of spent oil shale from surface retorting often have high viscosities making pumping difficult. These slurries tend to set up or harden rapidly, leaving little time to move the slurry to the appropriate position. These slurries also tend to shrink by sweating during the hardening stage, and sometimes weaken the solid mass and shrink from its position of support.
Lignosulfonate is sometimes added to concrete as a retarder to delay setting. Sodium silicate is sometimes added to concrete as a bleeding limiter or stabilizing agent. See Chemical Admixtures for Concrete, M. R. Rixom, E.&F.N. SPON. LTD. (1978). However, lignosulfonate and sodium silicate have not been used in compositions with spent oil shale from retorting. The properties of compositions of spent shales are not predictable from data on concrete because these compositions are new compositions of matter. The properties of such compositions must be determined empiracally.
It is an object of this invention to provide aqueous slurries of spent oil shale from surface retorting which can form solid, load bearing structures.
It is an object of this invention to provide aqueous slurries of spent oil shale from surface retorting which have retarded set-up time.
It is an object of this invention to provide aqueous slurries of spent oil shale from surface retorting which have reduced water leakage or bleeding.
It is an object of this invention to provide a method for forming coherent underground structures which may be load bearing and/or decrease water permeability.
It is an object of this invention to provide an improved method of mining minerals such as ores, coal, oil shale and the like.
It is an object of this invention to provide an improved method of stabilizing spent subterranean in situ oil shale retorts.